The integrity of an optical signal transmitted over long lengths of optical fiber degrades due to nonlinear interference (NLI) generated between different spectral components of the modulated optical field. Following detection, the NLI results in a noise-like degradation of the received signal that, in addition to amplified spontaneous emission (ASE) and other possible sources of noise in the receiver, increases the bit error rate and limits transmission reach. Unlike ASE, however, NLI is in principle predictable, and can be estimated for a known transmit data sequence and from the physical characteristics of the optical fiber link. If the complexity of an NLI estimation algorithm is sufficiently low, NLI can be compensated through appropriate digital signal processing (DSP) at either the transmitter or receiver of a coherent optical transmission system. For coherent transmission, the complexities of present methods of nonlinear pre-compensation grow rapidly with channel memory (in unit intervals, UI, or, equivalently, signalling intervals) to make implementation impractical for systems with channel memories exceeding 100 UI.
Techniques for addressing this limitation are desired.